Imaging of the human body using visible light has long been a desirable goal. In the late 1970s, dynamic light scattering theory was applied to living tissue to measure blood flow. Multiple scattering from the blood occurred, resulting in a Doppler broadening of the laser line width as revealed by the intensity fluctuations of the remitted speckles. This type of imaging worked fairly well, since the body behaved as a static matrix, and there was only occasional scattering from moving particles within the matrix. In about 1981, Bonner and Nossal at the National Institute of Health, wrote down the theory for imaging of blood flow using light, thereby formalizing the theory of "diffusing wave spectroscopy".
By the mid-1980s, diffusing wave spectroscopy was used to image optically dense systems in which all particles are moving, but the medium is generally viewed as homogeneous; that is, there are no spatial variations in the dynamic or optical properties. The aforementioned techniques for imaging with diffuse light are therefore limited since they cannot characterize media with spatially varying, dynamic properties, but can only characterize average properties of the media with well-defined boundaries.
Therefore, the imaging art has not provided a technique for imaging heterogeneous media. The aforementioned prior imaging techniques have only been able to determine dynamic and optical characteristics of a homogeneous medium, such as a dense colloid, wherein the magnitude of fluctuation of the intensities is obtained from the temporal intensity, or the correlation from an emerging speckle.
The current theory and devices for analyzing homogeneous media do not suffice for analyzing heterogeneous fluctuating media which are analogous to tumors, burns, and other real world structures found in the human body. There thus exists a long-felt but unsatisfied need in the art for a method of imaging spatially varying dynamic media which has not heretofore been satisfied.